DIABASE-PORPHYRITE. 85 
Tabulation of the results of a microscopic study of diabase-porphyrite and ashbed-diabase 
—Continued. 
| Angle between 
maximum ex- 
tinctions of 
adjacent hemi- 
z tropic bands of 
g = the plagioclase 
4 Place: 8 Macroscopic char- | Composition as determined by | in sections cut 
| 3 acters. the microscope. at random in 
a 3 ies the zone O: i. 
a a & 
: 2 | 3/3 | ¢ aseee cal 3 
3 g 3 E FI sides ‘of =e 
n Cln|AH]| & cross-hair. 
° ° ° 
907....| North shore of | SE. | 11 | 56|7W.| Minutely crystal- | Plagioclase; magnetite ; augite 
Lake Superior, 2 line; dark- in grains; unindividualized 
miles below the brown;semti-con- substance; very abundant red 
mouth of Bap- choidal fracture.| ferrite. 
tism River, Min- | 
nesota. | 
1051...! Bed of Cascade 23 | 62 | 2W.| Aphanitic; dark | Unindividualized substance; 
River, Minne- brown; conch- plagioclase needles; magnetite 
sota. oidal fracture; patches. 
an excessively 
| dense rock. 
1551...) North shore of 63 | 5E.| Aphanitic; dark- | Plagioclase; wunindividualized 
Lake Superior, reddish-brown; | substance; magnetite; augite, 
below Red Rock highly conch-| particles rare; much red fer- | 
Bay, Indian oidal fracture ; rite. 
reservation, comes out in 
Minnesota (not thin slabs. 
surveyed). 
1568...) Portage Bay Isl- Black; aphanitic; | Plagioclase, in matrix and in|3 (4 6 10 
and, north shore rough fracture. porphyritic crystals; magne- | il} 10 | 21 
of Lake Superior, tite; green and brown altera- | (24) 26 | 50 
| Minnesota. tion-products. 
(o) South side of Nearly aphanitic; | Minute tabular oligoclases pre- 
Michipicoten dark gray; con- dominant; magnetite; augite 
Island. choidalfracture;| in grains; some residuary 
no porphyritic magma. 
ingredients. 
(@) | Southwest side of Completely apha- | With a medium power this rock 
Michipicoten nitic; very dark- presents merely a pinkish- 
Island. gray; highly] tinted background, minutely 
conchoidal frac- dotted with gray, and no re- 
ture; no por- cognizable ingredients; with 
phyriticingredi- a higher power, in polarized 
ents. light, there are recognized ex- 
ceasively minute tabular plag- 
ioclases ; larger but still mi- 
nute magnetite particles; 
rare and excessively minute 
brightly polarizing particles 
which may belong to augite ; 
residuary magma predominat- 
ing, producing no effect what- 
ever between the crossed nicols. 
1 Macfarlane’s Michipicoten Collection, No. 2, ‘‘Compact Melaphyr.”” 
2Macfarlane’s Michipicoten Collection, No. 4, ‘Compact Melaphyr.” 
